the metadata is sourced externally via the exiftool command.
so first make sure you installed it on your system. the exact
command that is executed to create the view in the metadata expander
in lighttable mode is defined in the ~/.config/vkdt/config.rc file:
strgui/metadata/command:/usr/bin/exiftool -l -createdate -aperture -shutterspeed -iso
this default command will print in two line format (-l) the information
that follows after it. consult man exiftool for more options.